Fluid Jet Polishing, FJP, is a method of contouring and polishing a surface by aiming a jet of slurry at a component and eroding the surface to create a desired shape. Fluid jet polishing has been studied in some detail, in particular by Silvia M. Booij see ISBN 90-9017012-X, 2003.
A conventional fluid jet polishing system 1, illustrated in FIGS. 1 and 2, comprises a part holder 2 that holds a component 3 to be eroded, a contained area 4a with a drain 4b, a volume of working fluid 5, a pump 6 to pressurize the working fluid, plumbing 7 to return the working fluid to a nozzle 8, the nozzle 8 to direct the working fluid at the component 3, a motion system 10, usually computer controlled to direct the nozzle 8. The profile of the effect of a stationary fluid jet of the working fluid on the surface of the component 3 creates a tool pattern. A computer program is then used to optimize the dwell time of the tool pattern on the surface of the component 3 in order to achieve the desired final surface figure. Typically the pressure of the slurry of working fluid remains constant and the velocity (or dwell time) of the nozzle 8 is varied to remove the desired amount of material from different areas of the component 3. Alternatively the nozzle 8 can remain fixed and the component 3 can be moved. A temperature controller may be added to maintain the working fluid at a constant temperature
Another similar technology, disclosed in U.S. Pat. No. 5,951,369 issued Sep. 14, 1999 to Kordonski et al, is called Magneto Rheological Finishing, (MRF). The technology uses a liquid slurry that is directed to a wheel, where it is stiffened by magnetic fields. The stiff slurry is then carried by the wheel into contact with the component to be finished. After rubbing past the component and causing erosion the slurry is then returned to its liquid state for re-circulation by removal from the magnetic field. The advantage of MRF is that the stiffened slurry provides rapid material removal. The disadvantage is that the magnet and wheel technology makes the process significantly more complex and expensive than FJP.
Conventional FJP requires a uniform continuous stream of high pressure abrasive working fluid to erode the surface of a component. The working fluid contains small abrasive particles made from hard materials, such as Aluminum Oxide, Diamond or Zirconium Oxide. Almost all materials are effectively worn away by the eroding force of the high pressure abrasive fluid. Unfortunately, elements of the pumping systems are also quickly worn out by the eroding forces of the working fluid, making pump maintenance a significant cost in both time and materials. For example, pumping systems with high speed components or shafts, such as gear pumps, that rotate inside the working fluid slurry can wear out quickly, necessitating constant repair or replacement.
Other forms of pumps, such as diaphragm pumps or peristaltic pumps, cause a pulsation in the pressure and uneven erosion of the work piece, which is a particular concern for optical processing where nanometer level errors are significant.
An object of the present invention is to overcome the shortcomings of the prior art by providing a fluid polishing device including a pressure system providing constant pressure to the working polishing fluid without the need for mechanical parts moving within the working fluid.